1. Field of the Invention
The invention relates to a bleach activator, processes for its preparation and dry bleaching powders incorporating this activator.
2. The Prior Art
Dry bleaching powders for cleaning laundry generally contain inorganic persalts as the active component. These persalts serve as a source of hydrogen peroxide. In the absence of an activator, persalt bleach activity is undetectable where temperatures are less than 100.degree. F. and delivery dosages less than 100 ppm active oxygen. Activators have been recognized in the art as a method for effectuating bleaching under mild conditions.
U.S. Pat. No. 3,156,654 discloses heavy metal ions such as cobalt in combination with a chelating agent to catalyze peroxide decomposition. U.S. Pat. No. 3,532,634 suggests as effective persalt activators transition metals having atomic number 24 to 29 alongside a chelating agent. Neither process is totally satisfactory. Bare metal ions, even when chelated, accelerate wasteful decomposition reactions that are non-bleach effective. Under alkaline conditions, such as in laundry cleaning compositions, metal ions undergo irreversible oxidation. Perversely, the peroxide bleaching reaction is most effective at high pH. Another concern with soluble metal ion systems is the potential for ion deposition onto the fabric. Discoloration of fabric can occur where deposited metal ions undergo subsequent oxidation. Finally, the prior art metal ion catalysts are sensitive to water hardness. Their activity varies with the calcium and magnesium content of the water source.
Manganese (II) has been reported to be exceptionally effective in activating persalts under mild conditions. European Patent Application No. 0 082 563 discloses bleach compositions containing manganese (II) in conjunction with carbonate compounds. British Patent Application No. 82 36,005 describes manganese (II) in conjunction with a condensed phosphate/orthophosphate and an aluminosilicate as a bleach activator system. European Patent Application No. 0 025 608 reveals a peroxide decomposition catalyst consisting of acid treated zeolites or silicates whose cations have been exchanged for heavy metals such as manganese.
All the aforementioned activator systems still suffer from the presence of soluble manganese (II) ions. The soluble ions deposit on fabrics. Strong oxidants, such as hypochlorites, are frequently included in laundry washes. Deposited manganese will react to form highly staining manganese dioxide.
Consequently, it is an object of the present invention to provide a persalt manganese bleach activator that will not result in laundry staining.
A further object of this invention is to provide a process for the preparation of the manganese bleach activator.
Another object of this invention is to provide a laundry bleaching composition.